1. Field of the Invention
The present invention relates generally to printers and more particularly to a system for dissipating a build-up of static electric charge in thermal transfer printers during printing. The present invention also relates to a ribbon fold out mechanism mounted in the lid of a thermal printer to facilitate loading of ribbon media and printhead maintenance.
2. Prior Art
A thermal printer is normally provided with a printhead which comprises a large number of exothermic resistors arranged on an electrically insulating base. By selectively applying electric current to the exothermic resistors, heat is generated and applied to a thermo-sensitive print medium so as to print characters, pictures or both. The basic construction of a conventional thermal transfer printer includes a platen, thermal printhead, ribbon supply and take up mechanism, stepping motor and a gear train for driving the platen. A continuous strip of print media (e.g., paper, cloth, etc.) usually from a clamped print media roll is positioned between the platen and the ribbon with the thermal printhead caused to press the ribbon against the print media thereby printing characters or pictures on the print media strip using heat generated from the thermal printhead.
One of the most important aspects for the user in setting up a thermal transfer printer for printing is ribbon and media loading. Ribbon loading in conventional thermal transfer printers is a complicated, generally undesirable task which frequently involves ten or more steps. The usual steps are unlatching the printer, opening the lid of the printer, loading the ribbon supply roll, loading the ribbon take up roll, opening up the ribbon mechanism, threading the ribbon, wrapping the ribbon around the ribbon mechanism, taping it to the ribbon take up roll, taking up the ribbon slack, closing the lid of the printer and finally, re-latching the printer. Of the above-described steps, ribbon threading is usually the most difficult step to accomplish and as such can be a source of frustration for the user. Media loading usually requires the user to thread the media under or through the ribbon mechanism. Furthermore, conventional thermal transfer printers do not provide easy access to the thermal printhead for maintenance which adds to the overall cost of meeting the printing needs of the average user.
Electrostatic charge build-up has also been a long-standing problem associated with thermal transfer printing. Electrostatic charge build-up is mainly due to the motion of the ribbon as it passes between the printhead and a rotating rubber platen. The ribbon normally includes a Mylar(trademark) film which builds up significant amount of electrostatic charge as it moves past the printhead in close proximity to the linearly disposed electrical printing elements in the printhead which produce significant amount of heat during operation. This build-up of electrostatic charge can cause premature failure of the printhead and/or other components of the thermal transfer printer if not dissipated.
The conventional way of handling the electrostatic build-up problem in thermal transfer printers has been to ground the entire system using static brushes located proximate the thermal printhead. This type of setup adds complexity and cost to the printing system.
The present invention is directed to a system for automatically dissipating static electric charge build-up caused substantially by the passage of a moving ribbon between a rotating platen and a thermal printhead without the use of static brushes.
In accordance with one aspect of the present invention, the system comprises a ribbon frame made substantially of electrostatically dissipative material and adapted to support the thermal printhead proximate to the rotating platen, a power supply unit electrically coupled to the ribbon frame for grounding the ribbon frame to the power supply, and a printed circuit board assembly (PCBA) electrically coupled between the power supply and earth ground for grounding the power supply. The electrostatically dissipative material in the grounded ribbon frame automatically dissipates static electric charge as the moving ribbon comes into physical contact with at least one portion of the ribbon frame.
In accordance with another aspect of the present invention, the system comprises a ribbon frame made substantially of electrostatically dissipative material, a printhead bracket removably coupled to the ribbon frame and made substantially of the same electrostatically dissipative material wherein the printhead bracket is adapted to support the thermal printhead proximate to the rotating platen, and a printed circuit board assembly (PCBA) electrically coupled between the printhead bracket and earth ground for grounding the printhead bracket. The electrostatically dissipative material in the grounded printhead bracket automatically dissipates static electric charge as the moving ribbon comes into physical contact with at least one portion of the printhead bracket.
These and other aspects of the present invention will become apparent from a review of the accompanying drawings and the following detailed description of the preferred embodiments of the present invention.